Processing of electroslag refined metal

ABSTRACT

In a method and apparatus for the electroslag refining of metal, the method includes providing a refining vessel to contain an electroslag refining layer floating on a layer of molten refined metal. The refining vessel representing an upper part of a cooled mould comprises a plurality of superimposed sleeves which are electrically insulated from one another. The top sleeve, being the refining vessel, is substantially a non-consumable electrode and has a current lead electrically insulated from the sleeve. The molten electroslag layer is heated by a refining current which is passed from a power source through the mould and slag layer to the metal pool. An unrefined metal is lowered into the vessel into contact with the molten electroslag layer such that its surface is melted and overheated at the point of contact with the slag such that droplets of the metal are formed and these droplets pass down through the slag and are collected in a pool of molten refined metal beneath the slag.

This application claims priority of provisional application, Serial No.60/020,300, filed Jun. 24, 1996 and PCT application No. PCT/US97/10902,filed Jun. 24, 1997.

FIELD OF THE INVENTION

The present invention relates generally to direct processing of metalpassing through an electroslag refining operation. More specifically, itrelates to an apparatus and method having a split, insulated cruciblethat provides current through a non-consumable electrode with at leastone pair of symmetrical electrical leads in the electroslag processingapparatus. The invention further relates to atomizing, or otherwisedirectly processing a stream of refined metal, which stream is generateddirectly beneath an electroslag processing apparatus.

BACKGROUND OF THE INVENTION

It is known that the processing and refining of relatively large bodiesof metal, such as superalloys, are accompanied by many problems due tothe bulky volume of the body of metal itself. One such problem iscontrolling the grain size and other microstructure of the refinedmetals. Because the volume of the metal being refined is generally inthe order of about 5,000 to about 35,000 pounds or more, the refiningprocessing involves multiple steps, such as sequential heating andmelting, forming, cooling, and reheating of the large bodies of metal.Further, as processing by melting and similar operations is carried outon large bodies of metal, problems of segregation of the alloy elementsor ingredients of the metal also occur. Often, a lengthy and expensivesequence of processing operations is selected in order to overcome theabove-mentioned difficulties which arise through the use of bulkprocessing and refining operations of metals.

One such sequence of steps used in industry, involves vacuum inductionmelting; followed by electroslag refining; followed, in turn, by vacuumarc refining and followed, again in turn, by mechanical working throughforging and drawing. While the metal produced by such a sequence ishighly useful and the metal product itself is quite valuable, theprocessing sequence is quite expensive and time-consuming.

For example, vacuum induction melting of scrap metal into a large bodyof metal, such as between 20,000 to about 35,000 pounds or more, can bevery useful for the recovery of the scrap material. The scrap and othermetal is processed through the vacuum induction melting steps to form alarge ingot. Such a formed ingot has considerably more value than thescrap and other material used to form the ingot. However, in accordancewith the conventional vacuum induction melting process, the large ingotproduct is usually found to contain one or more of three types ofdefects: specially voids, slag inclusions, and macrosegregation.

The recovery of scrap metal into an ingot is usually the first step inan expensive, time-consuming metal refining process. Some of subsequentprocessing steps are specifically to cure the defects generated duringprior metal processing steps. For instance, after the scrap metal isformed into a large ingot, it then is often processed through anelectroslag refining step to remove oxides and sulfides. The product ofthe electroslag refining process containes lower concentrations of theseimpurities.

However, problems also occur during the conventional electroslagrefining process. Briefly, the conventional electroslag process includesa refining vessel containing a slag refining layer floating on a layerof molten refined metal. An ingot of unrefined metal is used as aconsumable electrode and is lowered into the vessel to make contact withthe molten electroslag layer. A refining current is passed through theslag layer to the ingot and causes surface melting at the interfacebetween the ingot and the slag layer. As the ingot is melted, oxideinclusions or impurities are exposed to the slag and removed from themetal at the point of contact between the ingot and the slag. Dropletsof refined metal are formed and these droplets pass down through theslag to be collected in a pool of molten refined metal beneath the slag.

The apparatus mentioned above, having an ingot as a consumableelectrode, includes a fixed relationship between the individualparameters of the process and, in particular, between the intensity ofthe refined current, the specific heat input, and the melting rate. Thisfixed relationship entails undesirable interdependence between the rateof electroslag refining of the metal, the metal ingot temperature andthe rate at which the refined molten metal is cooled. In addition, thereare problems concerning preparation of a large consumable electrodeingot. Further, in the past, it has been difficult for a conventionalelectroslag process utilizing a consumable electrode to provide activestirring of the metal and the slag. Thus, it would be desirable toprovide an apparatus that does not need to use a consumable electrodeingot. It is also desirable to provide an apparatus that increases theactive stirring of the metal and the slag to essentially improve therefining effect of the electroslag process.

Another problem of conventional electroslag refining is the formation ofa relatively deep metal pool in the electroslag crucible. This deep meltpool causes a varied degree of ingredient macrosegregation which leadsto a less desirable microstructure in the end product. To overcome thisdeep melt pool problem, a subsequent processing operation is employed incombination with the electroslag refining process. This latterprocessing may typically be vacuum arc refining. Vacuum arc refining isinitiated when the ingot produced by electroslag refining is processedthrough the vacuum arc steps to produce a relatively shallow melt poolwhereby an improved microstructure, perhaps also having a lower hydrogencontent, is produced. Following the vacuum arc refining process, theresulting ingot is then mechanically worked to yield a metal stockhaving a better microstructure. Such mechanical working may involve acombination of steps of forging and drawing. This thermo-mechanicalprocessing requires large, expensive equipment, as well as costlyamounts of energy input.

As pointed out, the drawbacks to using the above-recited combination ofprocess steps are many. Thus there is a need for a simplified, lesscostly, and time efficient method and apparatus for processing metals.

A method and apparatus which permit formation of relatively large ingotsof metal of uniform composition and desirably fine microstructurewithout the need for extensive processing has been previously suggestedby the General Electric Company in a number of patents (U.S. Pat. Nos.5,160,532; 5,310,165; 5,325,906; 5,332,197; 5,348,566 and 5,366,206).

The methods described in these patents involve a refining vesselcontaining an electroslag refining layer floating on a layer of moltenrefined metal with a consumable electrode ingot of unrefined metal. Thedroplets of the refined metal that are formed pass through the slag andare collected in a pool of molten refined metal beneath the slag. Thisrefined metal is held in a cold hearth. At the bottom of the coldhearth, a cold finger orifice permits the withdrawal of refined metalfrom the cold hearth apparatus. The refined metal passes as a streamfrom the cold finger orifice and is processed into a metal structurehaving desirable grain structure. A .preferred method for forming such astructure is by spray forming.

The above process described in the GE patents has the capability ofoperating continuously for an extended period of time and, accordingly,processing a large bulk of metal, if the rate of electroslag refining ofmetal and accordingly, the rate of delivery of the refined metal to thecold hearth approximate the rate at which molten metal is drained fromthe cold hearth through the cold finger orifice.

The apparatus utilized above, having an ingot as a consumable electrode,included a fixed relationship between individual parameters of theprocess and, in particular, between the intensity of the refinedcurrent, specific heat input and the melting rate. This fixedrelationship entails undesirable interdependence between the rate ofelectroslag refining of the metal, the metal temperature and the rate atwhich the molten metal is drained from the cold hearth through the coldfinger orifice. In addition, there are some problems concerningpreparation of a large consumable electrode metal ingot.

For all of the above-mentioned reasons, there is a need for a new andimproved electroslag refining apparatus and method to produce highquality, refined metal articles.

SUMMARY OF THE INVENTION

This need is satisfied by providing in the present invention a methodfor refining metal comprising the steps of: providing metal withnonspecification chemistry and microstructure; introducing the metalinto an electroslag refining vessel containing molten slag in a topsleeve of the vessel, said top sleeve of the vessel being anon-consumable electrode with at least one pair of symmetrical leads;contacting the molten slag in the vessel with the metal; passing asufficient amount of electric current through the slag for causing themetal to melt or overheat at surfaces where the metal contacts the slag;removing inclusions or impurities from the metal exposed to the slag;passing droplets of the metal formed from such melting or overheatingthrough the slag; collecting the descending molten metal in a hearthpositioned beneath the electroslag refining vessel. The inventive methodfurther comprises the step of: rotating or stirring the slag with themetal in the top sleeve of the refining vessel with an electromagneticforce. The electric current being passed through the slag with at leastone pair of symmetrical leads passes through a circuit comprising apower supply, the molten slag, and said refining vessel to causeresistance heating of the slag. The circuit can also include the liquidrefined metal. The electroslag composition is a salt containing calciumfluoride. In yet another aspect of the invention, the method furthercomprises the step of: providing a cold finger bottom pour spout at abottom of the hearth for permitting the liquid metal to pass through thespout as a metal stream. The rate at which molten metal is drained fromthe hearth is about equivalent to the rate at which metal is melted.Still yet, the invention comprises the step of: forming the metal streaminto an article having specification chemistry and microstructure. Thearticle can have a preform shape, be atomized into powder, cast into arod, spun into ribbon, or used as a filler metal for cladding orsurfacing.

The present invention in another of its broader aspects may beaccomplished by an apparatus for producing refined metal comprising ametal refining vessel adapted to hold a metal refining molten slag,means for supplying refining current to the molten slag, means forintroducing filler metal into the vessel in touching contact with themolten slag, electric supply means for supplying refining current to thetop sleeve of the vessel as a non-consumable electrode and through themolten slag and the metal pool to the current lead in the bottom sleeveof the vessel and for keeping the refining slag molten, a hearth beneaththe metal refining vessel, the hearth receiving and holding electroslagrefined molten metal in contact with a solid skull of the refined metalin contact with the hearth, a middle sleeve, operatively positionedbetween the metal refining vessel and the hearth, electrically insulatedtherefrom and including a control level mechanism. The top sleeve of thevessel further may comprise a means for rotating the molten slagtogether with the molten metal. The hearth may have a cold fingerorifice, operatively positioned below the hearth for receiving anddispensing as a stream, molten metal processed through the electroslagrefining process and through the hearth.

Still another aspect of the invention the formation of relatively largemetal ingots having a uniform composition and a desirable finemicrostructure without utilizing the extensive multistep process of theprior art.

Another aspect of the present invention provides a molten stream ofabove specification metal from below specification metal from formsincluding ingots, bars, tubes, plates, rods, etc., and also includingloose materials (powder, granules, shavings, pieces of irregularlyshaped metal) and liquid metal.

A further aspect of the present invention provides an apparatus andmethods for overcoming interdependence between the rate of electroslagrefining metal, metal temperature and the rate at which molten metal isdrained from the cold hearth through the cold finger orifice.

Still another aspect of the present invention is to provide apparatusand methods for actively stirring the metal and the slag.

Other advantages of the present invention will be apparent from thefollowing description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a detailed semi-schematic vertical sectional view of anapparatus suitable for carrying out the present invention;

FIG. 2 is a semi-schematic vertical sectional illustration of theapparatus of FIG. 1;

FIG. 3 is a fragmentary perspective view of a current supply electroslagrefining vessel used to rotate the slag, and metal; and

FIG. 4 is a semi-schematic illustration of the cold hearth apparatus ofFIG. 2 showing current lead of the bottom sleeve of the vessel.

DETAILED DESCRIPTION OF THE INVENTION

One method of the present invention is carried out by introducing fillermetal material to be refined, in the form of compact and loose material,and even liquid material, directly into an electroslag refiningapparatus and effectively refining the metal by way of active stirringand/or rotating of the melted metal and the slag. The melt of refinedmetals produced thereby is received and retained within a hearthapparatus mounted below the electroslag refining apparatus. The hearthis has cooled walls and is herein referred to as a cold hearth. Inanother aspect of the invention, the molten metal can then be dispensedfrom the cold hearth through a cold finger orifice mounted directlybelow the cold hearth reservoir. The metal can also remain in the hearthto solidify as a solid article.

Once the metal is drained from the cold hearth through the cold fingerorifice, it may be further processed to produce a relatively large ingotof refined metal or it may be processed through alternative processsteps to produce smaller articles or continuous cast articles such asstrip or rod or similar metallurgical products. Amorphous alloy productsmay be produced by processing a thin stream of melt exiting from thefinger orifice through a melt spinning operation in which the stream isdirected onto the outer rim of a spinning water cooled wheel. The metalstream can also be atomized to form a powder material. This methodeffectively eliminates many of the processing operations such as thosedescribed in the background statement above which have previously beennecessary in order to produce an end metal product having desiredproperties.

A very important aspect of the present invention is that it is nowpossible to avoid undesirable interdependence between the rate ofelectroslag refining of metal, metal and slag temperature and the rateat which metal is drained from the cold hearth through the cold fingerorifice during this process.

The process described herein is applicable to a wide range of alloyswhich can be beneficially processed through the electroslag refiningprocess. Such alloys include, but are not limited to, nickel andcobalt-based superalloys, titanium-based alloys, and ferrous-basedalloys, among others. The slag used in connection with such metals willvary with the metal being processed and will usually be the slagconventionally used with a particular metal in the conventionalelectroslag refining thereof.

Referring now particularly to the accompanying drawings, FIG. 1 is asemischematic elevational view of a number of the essential andauxiliary elements of a representative apparatus for carrying out thepresent invention. Referring now, first, to FIGS. 1 and 2, there are anumber of process stations and mechanisms including a vertical motioncontrol apparatus 10 shown schematically. The vertical motion controlapparatus includes a box 12 mounted to a vertical support 14, the boxcontains a motor or other mechanism for imparting rotary motion to ascrew member 16. A compact metal body support station 20 includes a bar22 threadedly engaged at one end to the screw member 16 at the other endand means for supporting the compact filler metal 24, such as, forexample, by conventional bolt means 26.

Conventional design filler feed mechanisms 1 and 2 for supplying loose18 or/and liquid 19 materials accordingly is positioned above thecrucible so as to feed metal into the slag bath.

An electroslag refining station 30 includes a water cooled vessel 32forming an open-end cavity containing a molten slag 34 and having atleast two leads 6 which connect the electroslag refining station to apower source, as described below.

For protection from spark erosion the station 30 has a lining 7 made ofelectrically conducting material. The lining is made of graphite. It isalso possible to make the lining of a refractory metal, such as tungstenor molybdenum.

The mould construction, or top sleeve of the refining vessel, being anon-consumable electrode is not itself a novel structure but has beendescribed in U.S. Pat. Nos. 4,185,682 and 4,305,451, the disclosures ofeach are herein incorporated by reference. In these patents, adescription is given of the mould having a single lead connected to thetop sleeve of the mould and to a power source. Such connection cannot bemade symmetrical about magnetic bodies that are located into theelectroslag power source outline which results in big energy losses inpower lines.

We have now devised a different structure from that disclosed in theabove-mentioned patents. The new structure has two or more symmetricalleads connected to the electroslag refining vessel and to a power sourcethat results in a considerable decrease in power losses. Additionally,the new structure includes an inner surface of the refining vessel formaking a surface check to close contact between the vessel and thelining of a refractory metal that results in uniform current density inthe slag pool.

The wall of the current supply water cooled vessel 32 may be providedwith at least one, and preferably at least two, radially orientedvertically extending open slots 8 filled with an electrically insulatingmaterial 9, e.g., asbestos or mica (FIG. 3). In this case, the vesselfunctions as a means for creating an electromagnetic field force whichcauses an unidirectional stable rotary motion or stirring of the moltenslag.

A middle sleeve 3 is mounted immediately below the electroslag refiningstation and it is of a height substantially smaller than the height ofthe electroslag refining station 30 and the lower cold hearth station40. It includes a water cooled vessel 4 and supplied with a controllevel mechanism 11 shown schematically. Between each pair of adjoiningsleeves 30, 3 and 3, 40, insulating gaskets 5 made, for instance, ofasbestos or mica are positioned. A skull of slag 75 may form along theinside surfaces of the inner wall 82 of the vessel 4 due to the coolingwater flowing against the outside surface of inner wall 82.

A cold hearth station 40 is mounted immediately below the middle sleeve3 and includes a water cooled hearth 42 containing a skull 44 ofsolidified refined metal and also a body 46 of liquid refined metal. Twocurrent leads 13 electrically isolated from the hearth 42 (FIG. 4) areprovided.

In one embodiment, the bottom opening structure 80 of the crucible isprovided in the form of a cold finger orifice. An optional station 50 isprovided immediately below the cold hearth station and the cold fingerorifice. This optional station has a gas orifice and manifold 52 whichgenerates streams of gas 54. These gas streams impact on a stream ofliquid metal 56 exiting from the cold finger structure 80 to produce aspray 58 of molten metal. The cold finger structure 80 has beenpreviously described in the US Patents incorporated by reference above.

As disclosed in the above-mentioned patents, the bottom openingstructure 80 combines a cold hearth with a cold finger orifice so thatthe cold finger structure effectively forms the center lower part of thecold hearth. In this case, the cold hearth mechanism permits thepurified alloy to form a skull by its contact with the cold hearth andthereby to serve as a container for the molten version of the samepurified alloy. In addition, the cold finger orifice structure 80provides a controllable skull 83 having a smaller thickness on theinside surface of the cold finger structure. As evident from FIG. 2, thethicker skull 44 in contact with the cold hearth and the thinner skull83 in contact with the cold finger structure are essentially continuous.

One reason why the skull 83 is thinner than 44 is that a controlledamount of heat may be put into the skull 83 and into the liquid metalbody 46 which is proximate the skull 83 by means of the inductionheating coils 85. The induction heating coil 85 is cooled by a coolingwater flowing through the coolant and power supply 87.

Induction heating power supplied to the coolant and power supply 87 froma power source 89 is shown schematically in FIG. 2. One significantadvantage of the construction of the cold finger structure 80 is thatthe heating effect of the induction energy penetrates through the coldfinger structure and acts on the body of liquid metal 46 as well as onthe skull 83 to apply heat thereto. This is one feature of the coldfinger structure and such feature depends on each of the fingers of thecold finger structure being insulated from the adjoining fingers by anair or gas gap or by an insulating material.

Because it is possible to control the amount of heating and coolingpassing from the induction coils 85 to and through the cold fingerstructure 80, it is possible to adjust the amount of heating or coolingwhich is provided through the cold finger structure both to the skull 83as well as to the body 46 of molten metal in contact with the skull.

The lowest station 60 is a spray collection station which includes asolid receiving surface such as ingot 62. The ingot 62 is supported by abar 64 mounted for rotary movement by motor 66 which, in turn, ismounted to a reciprocating mechanism 68 on a structural support 72.

Electric refining current is supplied by station 70 which includes anelectric power supply and control mechanism 74. Station 70 also includesa conductor 15 for carrying current to the electroslag refining vessel30 through leads 6. Conductor 78 carries current to the cold hearth 40through the leads 13 to complete the current circuit of the electroslagrefining mechanism. The leads 13 are electrically isolated from the coldhearth to cause current to flow through the metal skull heating theskull but not the cold hearth wall (FIG. 4). Station 70 also includes acurrent reversing mechanism 17 for introducing compact metal body in thecurrent circuit of necessity.

Referring now more specifically to FIG. 2, a more detailed view ofstations 30, 40 and 50 of FIG. 1 is illustrated. In general, thereference numerals as used in FIG. 2 correspond to the referencenumerals as used in FIG. 1 so that like parts bearing the same referencenumeral have essentially the same construction and function as wasdescribed with reference to FIG. 1.

Similarly, the same reference numerals are used with respect to the sameparts in the still more detailed views of FIGS. 3 and 4 discussed morethoroughly below.

As indicated above, FIG. 2 illustrates in greater detail the electroslagrefining vessel, the middle vessel, the cold hearth vessel, and thevarious apparatus associated with these vessels. As shown, the vesselsare double walled vessels having inner walls 36, 82 and outer walls 84,88. Between these two walls a cooling liquid such as water 86 isprovided as is conventional practice with some cold hearth apparatus.The cooling water 86 may be flowed to and through the flow channelbetween the inner wall 82 and outer wall 84 from supply means andthrough conventional inlet and other conventional means (not shown). Theuse of cooling water, such as 86, to provide cooling of the walls of thecold hearth station 40 is necessary in order to provide cooling at theinner wall 82 and thereby to cause the skull 44 to form on the innersurface of the cold hearth structure. The cooling water 86 is notessential to the operation of the electroslag refining or to the upperportion of the electroslag refining station 30 but such cooling may beprovided to insure that the liquid metal 46 will not make contact withthe inner wall 82 of the containment structure because the liquid metal46 could attack the wall 82 and cause some dissolution therefrom tocontaminate the liquid metal of body 46 within the cold hearth station40.

In operation, the apparatus of the present invention may best bedescribed with reference to FIG. 1. One feature of the presentinvention, illustratively shown in FIG. 1, concerns the throughputcapacity of the apparatus. As is indicated, the compact unrefined metalbody 24 together with loose 18 and/or liquid unrefined metal 19 may beprocessed in a single pass through the electroslag refining and relatedapparatus and through the atomization station 50 to form a relativelylarge volume ingot 62 through the spray forming process. Verysubstantial volumes of metal can be processed through the apparatusbecause the starting metals have relatively small concentrations ofimpurities such as oxides, sulfides, and the like, which are removed bythe electroslag refining process. The ingot 62 formed by the process, asillustrated in FIG. 1, is a refined ingot and is substantially free ofthe oxides, sulfides, and other impurities which are removed by theelectroslag refining of station 30 of the apparatus of FIG. 1.

While the process, as illustrated in FIG. 1, deals with the sprayforming of the ingot 62, it will be realized that the atomizationstation 50 may be employed simply to produce atomized metal. In thiscase, no ingot 62 is formed but rather the product of the process is theformation of powder which may be employed in conventional powdermetallurgy processing to form finished articles through well-knownestablished practice.

An alternative use of the apparatus, as illustrated in FIG. 1, is a meltspinning operation. Such melt spinning would omit the atomizationstation 50 and spray forming station 60 and would include thedisposition of a spinning water-cooled wheel to receive the melt 56 andto rapidly solidify and spin it into ribbon, as is known.

Depending on the application to be made of the electroslag refiningapparatus, as illustrated in FIG. 1, there is a need to control the rateat which a metal stream such as 56 is removed from the cold fingerorifice structure 80. The rate at which such a stream of molten metalmay be drained from the cold hearth through the cold finger structure 80is controlled by the cross-sectional area of the orifice and by thehydrostatic head of liquid above the orifice. This hydrostatic head isthe result of the column of liquid metal and of the liquid slag whichextends above the orifice of the cold finger structure 80. The flow rateof liquid from the cold finger orifice or nozzle has been determinedexperimentally for a cylindrical orifice.

It is apparent from the experiment that, if an electroslag refiningapparatus, such as illustrated in FIG. 2, is operated with a givenhydrostatic head, a nozzle area can be selected and provided whichpermits an essentially constant rate of flow of liquid metal from therefining vessel as long as the hydrostatic head above the nozzle ismaintained essentially constant. It is deemed important to the operationof such an apparatus that an essentially constant hydrostatic head beestablished and maintained. To provide such constant hydrostatic head,it is important that the melting rate of filler metal correspond to therate of withdrawal of metal in stream 56 from the refining vessel. Thismay be achieved by controlling the supply of liquid or loose fillermetal and corresponding changes of the refining current through controlmeans within box 12.

The rate at which the filler metal is refined in the apparatus of FIG. 1is determined by the level of refining power supplied to the vessel fromthe source such as 74 shown in FIG. 1. Such a current may be adjusted tovalues between about 1,000 to 20,000 amperes, and preferably betweenabout 2,000 to 12,000 amperes. The refining power supplied to, the slagmaintains and controls the heating and operating temperature of theslag. Thus, the temperature control of the slag is independent of therate of filler metal being added to the refining vessel.

In the described apparatus and method, generally a steady state isdesired in which the rate of metal melted and entering the refiningstation 30 as a liquid is equal to the rate at which liquid metal isremoved as a stream 56 through the cold finger structure. Slightadjustment to increase or decrease the rate of melting of metal are madeby adjusting the rate of introduction of the filler material into theslag.

What is claimed is:
 1. A method for electroslag refining comprising:introducing unrefined metal into an electroslag refining vesselcontaining a molten slag in a top sleeve thereof; electricallyinsulating said vessel from a cold hearth positioned beneath said vesselfor collecting molten metal from said vessel; forming a metal skull ofsolidified refined metal atop said hearth; conducting electrical currentto said vessel for forming a vessel electrode to carry said current inan electrical circuit through said molten slag and metal skull; andusing said electrical current conducted by said vessel to heat saidmolten slag and melt said unrefined metal for refining thereof as saidmolten metal descends through said slag and collects in said hearth. 2.The method according to claim 1 further comprising rotating or stirringthe slag with the metal in the top sleeve of the refining vessel with anelectromagnetic force.
 3. The method according to claim 2 comprising thestep of providing a cold finger bottom pour spout at a bottom of thehearth for permitting the molten metal to pass through the spout as ametal stream.
 4. The method of claim 3 where the stream of molten metalpassing from the cold finger orifice is atomized into powder.
 5. Themethod of claim 3 where the stream of molten metal passing from the coldfinger orifice is cast into rod.
 6. The method of claim 3 where thestream of molten metal passing from the cold finger orifice is melt spuninto ribbon.
 7. The method of claim 3 where the stream of molten metalpassing from the cold finger orifice is a filler metal for cladding orsurfacing.
 8. The method of claim 3 in which the rate at which moltenmetal is drained from said hearth is about equivalent to the rate atwhich the metal is melted.
 9. A refined article made by the method ofclaim
 2. 10. The method according to claim 1 further comprising the stepof providing a cold finger bottom pour spout at a bottom of the hearthfor permitting the molten metal to pass through the spout as a metalstream.
 11. The method of claim 10 where the stream of molten metal (56)passing from the cold finger orifice (80) is atomized into a preformarticle (62).
 12. The method of claim 10 where the stream of moltenmetal passing from the cold finger orifice is atomized into powder. 13.The method of claim 10 where the stream of molten metal passing from thecold finger orifice is cast into rod.
 14. The method of claim 10 wherethe stream of molten metal passing from the cold finger orifice is meltspun into ribbon.
 15. The method of claim 10 where the stream of moltenmetal passing from the cold finger orifice is a filler metal forcladding or surfacing.
 16. The method of claim 10 in which the rate atwhich molten metal (46) is drained from said hearth (40) is aboutequivalent to the rate at which metal is melted.
 17. The methodaccording to claim 1 where the electric circuit comprises a powersupply, the molten slag, and said refining vessel to cause resistanceheating of the slag.
 18. The method of claim 17 where the circuitincludes the body of molten metal.
 19. The method of claim 1 where theunrefined metal is a superalloy of nickel, cobalt or iron.
 20. Themethod of claim 1 where the unrefined metal is a titanium alloy.
 21. Themethod of claim 1 where the slag is a salt containing calcium fluoride.22. A refined article made by the method of claim
 1. 23. The method ofclaim 1 additionally comprising controlling introducing the unrefinedmetal to maintain essentially constant hydrostatic head of said moltenmetal within the vessel.
 24. The method of claim 1 additionallycomprising adjusting refining power to control passing the electricalcurrent to maintain a constant temperature control.
 25. The method ofclaim 1 further comprising passing the electrical current throughelectrically insulated leads to cause current to flow through a skull toheat the skull but not a wall of the hearth.
 26. A method forelectroslag refining comprising: introducing unrefined material into anelectroslag refining vessel containing a molten slag; electricallyinsulating said vessel from a cold hearth positioned therebelow todefine a vessel electrode; conducting electrical current in a circuitthrough said vessel, slag, and hearth to heat said slag; melting saidunrefined material in said molten slag to form molten metal; andcollecting said molten metal in said hearth after descending through andrefining by said slag.
 27. A method according to claim 1 furthercomprising: lowering said unrefined material into said vessel in contactwith said molten slag; and conducting electrical current in anothercircuit through said lowered unrefined material, slag, and hearth toheat said slag.
 28. A method according to claim 27 further comprisingprotecting said vessel from spark erosion by lining said vessel with anelectrically conducting material.
 29. A method according to claim 28wherein said electrical current is conducted through said vessel tocreate an electromagnetic force for stirring said slag and molten metaltherein.
 30. A method according to claim 29 further comprising:electrically insulating said vessel along a vertical slot extendingradially therethrough; and conducting said electrical current to saidvessel through two electrical leads connected to opposite diametricalsides of said vessel.
 31. A method according to claim 30 wherein saidelectrical current is conducted through said hearth through twoelectrical leads extending through said hearth on opposite diametricalsides thereof.
 32. A method according to claim 30 wherein said unrefinedmaterial comprises a consumable compact metal body electrode forconducting said electrical current therethrough.
 33. A method accordingto claim 32 further comprising additionally feeding loose unrefinedmaterial into said vessel for refining thereof.
 34. A method accordingto claim 32 further comprising additionally feeding liquid unrefinedmaterial into said vessel for refining thereof.
 35. A method accordingto claim 32 further comprising conducting said electrical currentthrough said consumable electrode in reverse from said vessel electrode.